U.S. patent number 6,497,760 [Application Number 09/896,751] was granted by the patent office on 2002-12-24 for modified soy protein adhesives.
This patent grant is currently assigned to Kansas State University Research Foundation. Invention is credited to Ke Bian, Xiuzhi Sun.
United States Patent |
6,497,760 |
Sun , et al. |
December 24, 2002 |
Modified soy protein adhesives
Abstract
Modified soy protein adhesives are provided which have increased
bonding abilities. The adhesives are prepared by forming a
dispersion of soy protein, water, and a modifier selected from two
classes of modifiers. The preferred modifiers are urea, sodium
dodecylbenzene sulfonate, sodium dodecyl sulfate, and guanidine
hydrochloride. The resulting dispersion is stirred, freeze-dried,
and milled into a powder to be stored until use. The adhesives of
the invention have superior bonding qualities while being safe for
the environment. The urea-modified, GH-modified, SDS-modified, and
SDBS-modified soy protein adhesives have higher water resistance
than non-modified soy protein adhesives.
Inventors: |
Sun; Xiuzhi (Manhattan, KS),
Bian; Ke (Henan, CN) |
Assignee: |
Kansas State University Research
Foundation (Manhattan, KS)
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Family
ID: |
26828695 |
Appl.
No.: |
09/896,751 |
Filed: |
July 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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337294 |
Jun 21, 1999 |
|
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130667 |
Aug 7, 1998 |
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Current U.S.
Class: |
106/131.1;
156/336; 530/408; 530/409; 428/478.4 |
Current CPC
Class: |
C09J
189/00 (20130101); C09J 189/00 (20130101); Y10T
428/31772 (20150401); C08L 2666/28 (20130101); C08L
2666/28 (20130101) |
Current International
Class: |
C09J
189/00 (20060101); C08L 003/00 () |
Field of
Search: |
;156/336 ;106/131.1,FOR
132/ ;428/478.4 ;430/408,409 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gallagher; John J.
Attorney, Agent or Firm: Hovey Williams LLP
Parent Case Text
RELATED APPLICATIONS
This is a continuation of application Ser. No. 09/337,294, filed
Jun. 21, 1999, now abandoned which is a continuation-in-part of
application Ser. No. 09/130,667, filed Aug. 7, 1998, now abandoned.
Claims
We claim:
1. A soy protein-based adhesive comprising a quantity of soy
protein isolate reacted in an aqueous system with a modifier to
form a soy protein isolate slurry, said modifier being guanidine
hydrochloride, said adhesive having the property of adhering wooden
adherends together such that the bond exhibits a shear strength of
at least about 30 kg/cm.sup.2, using ASTM Method D-906.
2. A process for producing an adhesive comprising the steps of: (a)
providing a quantity of previously prepared soy protein isolate;
and (b) mixing said soy protein isolate with a modifier to form a
protein slurry and causing said modifier to react with said soy
protein isolate to form a soy protein isolate- modifier adhesive,
said modifier being guanidine hydrochloride.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with modified soy
protein adhesives, and methods of production and use thereof. More
particularly, the invention relates to such adhesives produced by
the reaction of soy protein with a modifier selected from two
classes of compounds in an aqueous system wherein the adhesives
exhibit higher water resistance than non-modified soy protein
adhesives. In the use of the adhesives of the invention, the bonds
between the adherends have high shear strengths. The adhesives are
preferably formulated by mixing a quantity of soy protein with an
aqueous dispersion comprising the modifier and reacting the
mixture; the resultant adhesive may be used in a liquefied form or
dried to a reconstitutable powder.
2. Description of the Prior Art
Large quantities of adhesives are used annually for such things as
interior and exterior applications of plywood and particle board,
paper manufacturing, book binding, textile sizing, abrasives,
gummed tape, and matches. Petroleum-based and soy protein-based
adhesives are two general types of adhesives used in such
applications. Soy protein adhesives known in the art generally lack
the gluing strength and water resistance compared to
petroleum-based adhesives. Most of the petroleum-based adhesives,
however, contain phenol formaldehyde which is harmful to the
environment. Also, petroleum resources are naturally limited and
politically controlled. Furthermore, petroleum-based adhesives are
not biodegradable thus resulting in an unwanted accumulation of
waste. As a result, soy protein polymers are being reconsidered as
an alternative adhesive to reduce the usage of petroleum polymers
and to prevent environmental pollution.
In soy protein-based adhesives, the protein molecules are
dispersed, and thus partially unfolded, in dispersion. The unfolded
molecules increase the contact area and adhesion of the protein
molecules onto other surfaces and entangle each other during the
curing process to provide bonding strength. However, while soy
protein-based adhesives are environmental friendly and are derived
from soybeans which are renewable and more abundant than petroleum
resources, the currently available soy protein-based adhesives lack
the increased gluing strength and water resistance which are
advantageous in typical adhesive applications.
SUMMARY OF THE INVENTION
The present invention overcomes the problems noted above, and
provides a soy protein-based adhesive having increased bonding
abilities and high water resistance. The adhesives of the invention
are formed by modifying soy protein (SP), preferably derived from
soy protein isolate (SPI) with certain compounds (modifiers).
Two classes of mild chemical modifiers are preferred in the
preparation of the adhesives of the invention. One preferred
modifier class includes saturated and unsaturated alkali metal
C.sub.8 -C.sub.22 sulfate and sulfonate salts. Even more preferred
are saturated and unsaturated alkali metal C.sub.10 -C.sub.18
sulfate and sulfonate salts. Saturated alkali metal C.sub.8
-C.sub.22 sulfate and sulfonate salts include all alkali metal
alkyl (such as octyl and dodecyl) C.sub.8 -C.sub.22 sulfate and
sulfonate salts. Unsaturated alkali metal C.sub.8 -C.sub.22 sulfate
and sulfonate salts include all alkali metal alkenyl (such as
decenyl and octadecenyl) C.sub.8 -C.sub.22 sulfate and sulfonate
salts and all alkali metal alkynyl (such as octynyl and
tetradecynyl) C.sub.8 -C.sub.22 sulfate and sulfonate salts. Two
particularly preferred modifiers in this class are sodium dodecyl
sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS).
Another preferred class of modifiers for forming the adhesives of
the invention are those compounds having the formula I:
##STR1##
wherein each R is individually selected from the group consisting
of H and C.sub.1 -C.sub.4 saturated and unsaturated groups, and X
is selected from the group consisting of O, NH, and S. The C.sub.1
-C.sub.4 saturated and unsaturated groups refers to alkyl groups
(both straight and branched chain) and unsaturated refers to
alkenyl and alkynyl groups (both straight and branched chain). The
preferred modifiers in this class are urea and guanidine complexed
with hydrochloride.
Advantageously, the adhesives of the invention can be formed by
utilizing mixtures of the foregoing modifiers. These mixtures can
be within a class or they can contain modifiers from each class.
For example, the modifier could be a mixture of urea and guanidine
hydrochloride (which fall within the same class) or a mixture of
urea and SDS.
When urea or guanidine hydrochloride (GH) is the modifier used to
form the adhesives of the invention (hereinafter referred to as
urea-modified soy protein adhesives or U-SPI and guanidine
hydrochloride-modified soy protein adhesives or GH-SPI,
respectively), the adhesives are preferably formed by preparing a
mixture comprising (and preferably consisting essentially of) urea
or guanidine hydrochloride (GH) and water with a quantity of soy
protein thus forming a slurry or dispersion. Any source of soy
protein (such as soybean concentrate or soybean meal) is suitable
for making the adhesives of the invention, but a particularly
preferred source of soy protein is soy protein isolate. The soy
protein is preferably essentially free of urease, having less than
about 10 activity units of urease. When urea is the modifier, the
amount thereof should result in a urea content of at least about 6%
by weight, preferably at least about 10% by weight, and more
preferably at least about 15-18% by weight, based on the weight of
the protein slurry. The amount of urea utilized is important in
order to be certain that the protein molecules properly unravel in
dispersion, thus increasing the contact area of the molecules as
well as their adhesion onto other surfaces. These unraveled
molecules will then entangle with each other during the curing
process contributing to the increased bonding strength of the
adhesives.
The resulting soy protein-urea or soy protein-GH aqueous dispersion
is normally mixed for about 60 minutes. The forming of and mixing
of the slurry is carried out at a temperature of from about 10 to
about 80.degree. C., and preferably from about 20 to about
50.degree. C. Even more preferably, the forming and mixing of the
dispersion takes place under ambient temperature and pressure
conditions. The dispersion should have a pH of less than about 8,
and more preferably less than about 7 (e.g., from about 2-7). After
mixing, the reacted dispersion can be immediately used as an
adhesive, or it can be freeze-dried, milled into a powder, and
stored for later use. Or, if freeze-drying is not practical, the
dispersion can be subjected to any known mechanism or process (such
as spray drying) by which the moisture is substantially removed.
This is just one example of how to form a modified soy protein
adhesive utilizing a modifier (i.e., urea or GH) within this class
of preferred modifiers. Any other modifiers having the formula I
can be made in the same fashion, with appropriate process
modifications depending upon the specific modifier chosen.
When sodium dodecyl sulfate or sodium dodecylbenzene sulfonate is
the modifier used to form the adhesives of the invention
(hereinafter referred to as SDS-SPI and SDBS-SPI adhesives,
respectively), the process of forming the adhesives comprises
mixing soy protein and water at room temperature for about 30
minutes to form a suspension or dispersion. Any source of soy
protein (such as soybean concentrate or soybean meal) is suitable
for making the adhesives, but a particularly preferred source of
soy protein is soy protein isolate. SDS or SDBS is added to the
suspension with the resulting dispersion being stirred for about 6
hours. Preferably, the SDS or SDBS is present in the resulting
dispersion at a level from about 0.1 to about 15% by weight, and
more preferably from about 0.5 to about 6% by weight based on the
weight of said protein slurry. Preferably, the forming of the
adhesive takes place under ambient temperature and pressure
conditions. The final slurry should have the same pH ranges as the
urea adhesives, and likewise such adhesives can be used in liquid
or dried particulate form. This is just one example of how to form
a modified soy protein adhesive utilizing a modifier (i.e., SDS or
SDBS) which falls with the class of saturated and unsaturated
alkali metal C.sub.8 -C.sub.22 sulfate and sulfonate salts. Other
adhesives made using modifiers within this class can be formed in a
similar manner with appropriate process modifications depending
upon the specific modifier chosen.
Regardless of the modifier utilized, the final dried adhesive
powders should be small enough so that 90% of the powder particles
pass through a 50 mesh screen, and preferably the powder particle
size is such that 90% of the powder particles pass through a mesh
screen having a size of at least about 100 mesh or higher ("higher"
meaning e.g., 150 mesh or 200 mesh). The adhesive powders of the
invention can be stored in powder form until the point-of-use. When
the adhesive is needed, the powder is added to water (preferably
distilled water) at a ratio of from about 1:20 to about 1:4, and
preferably at a ratio of about 1:6 of SP powder:water. The powder
is dispersed in the water at room temperature for about five
minutes, preferably while heating to at least about 50.degree. C.
The resulting aqueous adhesive can then be applied to an adherend
by any conventional application means, such as by brushing the
adhesive onto a surface of the adherend, or by placing the adhesive
between and in contact with a pair of adherends. Preferably the
adhesive application is followed by compressing of the adherends in
order to facilitate adhesion.
In some applications, it may be desirable to modify a soy flour
having at least about 50% protein to form the adhesives of the
invention. Suitable modifiers for include all of those set forth
above, with the exception of urea (because soy flours contains
appreciable quantities of urease). Guanidine hydrochloride, SDS,
and SDBS are particularly preferred for modifying soy flours. The
modified soy flours have improved water resistance and gluing
strengths as compared to non-modified soy flours.
The adhesives of the invention are particularly useful for adhering
cellulosic components, such as those formed of wood or paper. The
amount of adhesive necessary can be varied as required by the
characteristics of the adherends. When the adhesives of the
invention are applied to wooden adherends, the gluing strength
(i.e., the shear strength) of the adhesive is at least about 30
kg/cm.sup.2, preferably at least about 50 kg/cm.sup.2, and more
preferably about 65 kg/cm.sup.2.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 compares the viscosity of U-SPI having a solids
concentration of 16% to the viscosity of non-modified soy proteins
having a solids concentration of 16%, as measured by a rapid
viscosity analyzer; and
FIG. 2 illustrates the differential scanning calorimeter curves of
a soy protein slurry having a solids concentration of 16% and a
urea concentration of 0M, 2M, 4M, 6M, and 8M.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples set forth preferred aspects of the present
invention. It is to be understood, however, that these examples are
provided by way of illustration and nothing therein should be taken
as a limitation upon the overall scope of the invention.
EXAMPLE 1
Preparation of the Samples
1. Urea-Modified Soy Protein Isolate (U-SPI)
Ten grams of SPI powder was added to 150 ml of 3.2 N urea-distilled
water and stirred at room temperature for about one hour. The
mixture was freeze-dried and milled into a powder.
2. Sodium Dodecyl Sulfate-Modified Soy Protein Isolate
(SDS-SPI)
Fifty grams of SPI powder was added to 500 ml of distilled water
and the solution was mixed at room temperature for about 30 minutes
to form a uniform suspension. Twenty milliliters of a solution
containing 25% SDS was added to the suspension followed by stirring
for about 6 hours. The resulting slurry was freeze-dried and milled
into a powder.
3. Alkali-Modified Soy Protein Isolate (A-SPI)
A-SPI was prepared as described by Hettiarachchy et al., JAOCS,
72(12):1461-1464 (1995), incorporated by reference herein. Briefly,
30 grams of SPI powder was added to 400 ml of distilled water and
mixed at room temperature for about two hours. Sodium hydroxide was
added to the resulting mixture in order to adjust the mixture pH to
11. The mixture was stirred at 50.degree. C. for another two hours
to hydrolyze the SPI. The mixture was then freeze-dried and milled
into a powder.
4. Heat-Treated Soy Protein Isolate (H-SPI)
In order to observe the effect of heat treatment on adhesive
properties, 30 grams of SPI powder was added to 400 ml of distilled
water. The resulting mixture was stirred at 50.degree. C. for about
two hours followed by freeze-drying and milling into a powder. No
sodium hydroxide was added to this sample.
5. Wood Samples
The wood samples used in these tests were pine, maple, poplar, and
walnut. Each wood sample had dimensions of approximately 3
mm.times.20 mm.times.50 mm (thickness.times.width.times.length). A
3-piece wood was used to prepare the testing specimens. The 3-piece
wood comprised a base piece of wood and a second piece of wood
having one of its sides positioned along one side of the base wood.
The side of the second piece of wood overlapped the side of the
base piece of wood by 20 mm, with the base wood being below the
second piece. The base wood and second piece of wood were adhered
to one another by the inventive adhesive which was applied to the
overlapped portion. This arrangement was repeated with a third
piece of wood which was placed along the side of the base wood
remote from the adhered second piece, again with the base wood
being below the second piece. Tensile strengths (discussed below)
of the glued 3 piece wood samples were determined by applying force
to the second piece of wood in a direction away from the third
piece of wood while simultaneously applying force to the third
piece of wood in a direction away from the second piece of wood.
The force at which the adhered portions separated was recorded.
Application of Adhesives to the Wood Samples
The previously prepared modified SPI powders were each separately
added to distilled water at a ratio of 1:6 (SPI powder:water) and
mixed at room temperature for about five minutes. The resulting
adhesive slurry was brushed onto each wood sample until the sample
was completely wet, and the concentration of the protein on the
wood surface was about 1.5 mg/cm.sup.2. The slurry-brushed wood
samples were kept at room temperature for about five minutes after
which they were pressed by a hot press (Model 3890 Auto "M", Carver
Inc., Wabash, Ind.) at a press temperature of 104.degree. C. and
pressure of 20 kg/cm.sup.2 for about 15 minutes. The samples were
placed in a plastic bag and maintained at ambient conditions until
further analyses were performed.
Adhesive Quality Measurements
Shear strength was determined following ASTM standard method D-906
utilizing an Instron testing machine (Model 4466, Canton, Mass.)
with a crosshead speed of 2.4 cm/min. The maximum shear strength at
the point of breakage was recorded.
Water resistance of the adhesives (for exterior applications) was
tested using the modified method as described by Hettiarachchy et
al. (1995). Briefly, the specimen was soaked in tap water at room
temperature for about 48 hours. The soaked specimen was then dried
at room temperature in a fume hood for about 48 hours, and the
delamination of the sample was determined. This procedure was
repeated two more times.
Water resistance of the adhesives (for interior applications) was
tested using two cycles as set forth in ASTM standard method
D-1183. Briefly, in the first cycle, the sample was conditioned in
a chamber at 90% relative humidity (RH) and 23.degree. C. for about
60 hours with the shear strength being determined at this time. The
sample was then conditioned at 25% RH and 48.degree. C. for about
24 hours with the shear strength being tested again. In the second
cycle, the sample was conditioned in a chamber at 90% RH and
23.degree. C. for about 72 hours with the shear strength being
determined at this time. The sample was then conditioned at 25% RH
and 48 .degree. C. for 48 hours, and the shear strength was tested
again.
Results and Discussion
Table I sets forth the shear strength of the wood specimens glued
with both non-modified SPI (food grade soy protein isolate
available from Archer Daniels Midland, Decatur, Ill.) and modified
soybean protein adhesives. The gluing strengths of all modified SPI
adhesives were strong for walnut, maple, and poplar wood samples,
being in the range of 50 to 64 kg/cm.sup.2.
TABLE I Shear strength (kg/cm.sup.2) of wood specimens glued with
non-modified and modified soy protein adhesives. Sample U-SPI
SDS-SPI A-SPI H-SPI SPI.sup.a Walnut 59.74 54 59.62 54.48 39.1
Maple 57.66 -- 64.5 56.2 50.42 Poplar 62.26 -- 63.94 49.22 46.2
Pine 31.34 45 30.0 27.50 35.50 .sup.a Food grade soy protein
isolate available from ADM.
Table II sets forth the delamination data after three cycles of the
water soaking tests. The control specimens had the highest water
absorption and the walnut and poplar control specimens were 100%
delaminated, while the A-SPI specimens were 40-80% delaminated.
Although none of the U-SPI or SDS-SPI specimens for the walnut and
pine wood samples were delaminated, the maple and poplar U-SPI
specimens were 20% and 40% delaminated, respectively. This is
attributable to the fact that maple and poplar have higher
shrinkage stress than walnut and pine wood samples. Maple and
poplar had about 16% bulk volume increase after 48 hours of water
soaking, which was higher than the 11% with walnut and pine. The
maple and poplar samples had a linear expansion of from 6.3 to 7.6%
which was higher than the linear expansion of 4.6% for walnut and
pine.
The microstructure from scanning electron microscopy (SEM)
indicated that the surface structure of pine consisted of
well-oriented strips (i.e., smooth and neat) compared to the
surface structure of walnut, maple, and poplar which was rough and
randomly oriented. Though not wishing to be bound by theory, it is
believed that the lower gluing strength obtained with the pine
samples is a result of the surface structure.
TABLE II Delamination (%) of wood specimens after three cycles of
water soaking tests. Sample U-SPI SDS-SPI A-SPI H-SPI SPI.sup.a
Walnut 0 0 40 60 100 Maple 20 -- 60 80 80 Poplar 40 -- 80 80 100
Pine 0 0 60 60 80 .sup.a Food grade soy protein isolate available
from ADM.
After 60 hours of incubating in a humidity chamber at 90% RH, the
gluing strength was not reduced, but rather was increased slightly
for the U-SPI, SDS-SPI, A-SPI, and H-SPI modified adhesives (see
Table III compared to Table I). Water absorbed during incubation
might act as a plasticizer resulting in high hydrogen bonding
between protein molecules.
TABLE III Shear strength (kg/cm.sup.2) of wood specimens after 90%
RH incubation at 23.degree. C. for 60 hours. Sample U-SPI SDS-SPI
A-SPI H-SPI SPI.sup.a Walnut 63.8 55 60.4 57.50 46.6 Maple 53.8 --
64.5 54.66 44.2 Poplar 64.2 -- 64.42 54.46 44.3 Pine 30.1 45 46.72
35.72 27.0 .sup.a Food grade soy protein isolate available from
ADM.
With the samples that were incubated at 90% RH at 23.degree. C. for
60 hours followed by 24 hours of incubation at 25% RH at 48.degree.
C., the gluing strength significantly decreased for A-SPI and H-SPI
adhesives (see Table IV). The gluing strength for U-SPI and SDS-SPI
remained the same for maple and poplar wood samples. However, the
gluing strength of U-SPI adhesives on walnut was reduced to about
38 kg/cm.sup.2. The microstructure of the walnut surface may cause
the strength reduction upon wetting. The gluing strengths of most
of these samples remained the same after the second incubation
cycle treatment as shown in Table V.
TABLE IV Shear strength (kg/cm.sup.2) of wood specimens after first
cycle incubation - 90% RH, 23.degree. C., 60 hours and 25% RH,
48.degree. C., 24 hours. Sample U-SPI SDS-SPI A-SPI H-SPI SPI.sup.a
Walnut 38.24 48 40.74 50.1 40.74 Maple 57.0 -- 48 40.5 39.5 Poplar
63.24 -- 50.0 42.74 47.0 Pine 31.74 44 42.74 25.0 29.26 .sup.a Food
grade soy protein isolate available from ADM.
TABLE V Shear strength (kg/cm.sup.2) of wood specimens after second
cycle incubation - 90% RH, 23.degree. C., 72 hours and 25% RH,
48.degree. C., 24 hours. Sample U-SPI SDS-SPI A-SPI H-SPI SPI.sup.a
Walnut 37.16 45 40.1 39.4 35.0 Maple 57.46 -- 45.4 41.00 41.88
Poplar 53.28 -- 50.0 43.34 41.3 Pine 30.74 42 39.26 24.00 26.32
.sup.a Food grade soy protein isolate available from ADM.
Therefore, the urea-modified and SDS-modified soy protein adhesives
were excellent adhesives because they had higher bonding strengths
and lower water absorptions while retaining the environmentally
safe characteristics of the unmodified soy protein adhesives.
EXAMPLE 2
U-SPI adhesive was prepared as described in Example 1. The wood
samples used in this test were walnut, pine, and cherry. Each wood
sample had dimensions of approximately 3 mm.times.20 mm.times.50 mm
(thickness.times.width.times.length). At least five samples of each
type of wood were utilized. The procedures by which the U-SPI
adhesive was applied to the wood samples were exactly as described
in Example 1.
Wood samples of each wood type were soaked in water at room
temperature for 24 hours, 48 hours, and 72 hours, respectively.
After the respective soaking, the shear strength of each sample was
determined and is set forth in Table VI below.
TABLE VI Shear strength (kg/cm.sup.2) of wood samples glued with
U-SPI adhesive after water soaking. Sample 24 HOURS 48 HOURS 72
HOURS Walnut 48.2 48 43.5 Pine 22.5 22.3 20.75 Cherry 55 49
54.5
EXAMPLE 3
U-SPI adhesive was prepared as described in Example 1. A cherry
wood sample was prepared and adhesive applied as described in
Example 2. The water resistance of the adhesive (for exterior
applications) was tested using the modified method as described by
Hettiarachchy et al. (1995) and as described in Example 1. There
was no delamination of the cherry wood glued with the U-SPI
adhesive.
EXAMPLE 4
This test was conducted to determine the viscosity and thermal
stability of urea-modified soy protein adhesives compared to the
viscosity and thermal stability of non-modified soy protein
adhesives. U-SPI adhesive was prepared as described in Example 1. A
sample of the U-SPI adhesive and a sample of a non-modified soy
protein adhesive (food grade SPI available from ADM) were tested on
a rapid viscosity analyzer (RAV). The results, shown in FIG. 1,
indicate that the U-SPI adhesive has a lower viscosity and is more
stable thermally than the non-modified soy protein adhesives. This
means that the adhesives of the invention may be applied more
easily and have a longer working life with greater thermal
stability compared to non-modified soy protein adhesives.
EXAMPLE 5
U-SPI adhesives (having a 16% solids content) were prepared
following the procedure described in Example 1, but varying the
quantities of urea to achieve adhesives having concentrations of
2M, 4M, 6M, and 8M of urea. The thermal transitions of the modified
adhesives were measured with a differential scanning calorimeter
(DSC). These transitions were compared to the thermal transitions
of non-modified soy protein adhesives having a 16% solids content
(food grade SPI available from ADM). The calorimeter used was a
Perkin-Elmer DSC 7 instrument (Perkin-Elmer, Norwalk, Conn.)
calibrated with indium and zinc. The DSC temperature scan range was
from 20.degree. C. to 180.degree. C. at a heating rate of
10.degree. C./min. A large DSC pan was used to hold the
samples.
The thermal transition peaks of the U-SPI adhesives are shown in
FIG. 2. The area of the thermal transition peak of a DSC curve
corresponds to the protein structure and denaturation of the
sample. In FIG. 2, the non-modified soy protein adhesive (i.e., 0M
urea) gave the largest peak area. The peak area decreased as the
urea concentration increased. These results confirm that urea
modifies the soy protein structure.
EXAMPLE 6
SDS-SPI adhesives having varying concentrations of SDS were
prepared. During these tests, a solution was prepared containing
0.5% SDS and 99.5% distilled water. To this solution, 10 g of SPI
powder was added, and the resulting suspension was mixed for about
6 hours. A similar procedure was followed to prepare 1% by weight
SDS-SPI adhesives and 3% by weight SDS-SPI adhesives. The wood
samples used in these tests were cherry, pine, and walnut. Each
wood sample had dimensions of approximately 3 mm.times.20
mm.times.50 mm (thickness.times.width.times.length). The procedures
by which the SDS-SPI adhesive was applied to the wood samples were
exactly as described in Example 1. Table VII sets forth the shear
strength of the wood specimens glued with the SPS-SPI and the
non-modified SPI as determined following the procedures set forth
in Example 1.
TABLE VII Shear strength (kg/cm.sup.2) of wood specimens glued with
non-modified and sodium dodecyl sulfate (SDS) (0.5%, 1%, and
3%)-modified soy protein adhesives. Sample 0.5% SDS-SPI 1% SDS-SPI
3% SDS-SPI SPI.sup.a Cherry 54 .+-. 8 55 .+-. 7 38 .+-. 9 41 .+-. 7
Pine 46 .+-. 5 45 .+-. 3 42 .+-. 6 31 .+-. 4 Walnut 52 .+-. 9 54
.+-. 10 37 .+-. 7 30 .+-. 12 .sup.a Food grade soy protein isolate
available from ADM.
EXAMPLE 7
SDS-SPI adhesives and wood samples were prepared as described in
Example 6. In these tests, the shear strength of the wood specimens
was determined after the samples were incubated at 90% RH for 72
hours at 23.degree. C. followed by incubation at 25% RH for 24
hours at 48.degree. C., with this cycle then being repeated twice.
These results are set forth in Table VIII below.
TABLE VIII Shear strength (kg/cm.sup.2) of wood specimens glued
with non-modified and sodium dodecyl sulfate (SDS) (0.5%, 1%, and
3%)-modified soy protein adhesives after incubation aging test.
Sample 0.5% SDS-SPI 1% SDS-SPI 3% SDS-SPI SPI.sup.a Cherry 45 .+-.
8 50 .+-. 9 30 .+-. 8 38 .+-. 5 Pine 43 .+-. 8 43 .+-. 9 37 .+-. 7
21 .+-. 8 Walnut 44 .+-. 6 46 .+-. 8 26 .+-. 7 25 .+-. 9 .sup.a
Food grade soy protein isolate available from ADM.
EXAMPLE 8
SDS-SPI adhesives and wood samples were prepared as described in
Example 6. In these tests, the % delamination was determined after
subjecting the specimens to three cycles of water soaking as
described in Example 1. The SDS-SPI specimens each had 0%
delamination while the non-modified samples had 90-100%
delamination.
TABLE IX Delamination (%) of wood specimens glued with non-modified
and sodium dodecyl sulfate (SDS) (0.5%, 1%, and 3%)-modified soy
protein adhesives after water soaking test. Sample 0.5% SDS-SPI 1%
SDS-SPI 3% SDS-SPI SPI.sup.a Cherry 0 0 0 100 Pine 0 0 0 90 Walnut
0 0 0 100 .sup.a Food grade soy protein isolate available from
ADM.
EXAMPLE 9
SDS-SPI adhesives and wood samples were prepared as described in
Example 6. These specimens were subjected to three cycles of water
soaking. The samples' shear strength was then determined following
the procedures set forth in Example 1. Table X sets forth the
results of these tests. While the shear strength did decrease
somewhat compared to the shear strength of the samples which were
not subjected to any water soaking tests, the SDS-SPI adhesives
showed much greater shear strength than did the non-modified
samples.
TABLE X Shear strength (kg/cm.sup.2) of wood specimens glued with
non-modified and sodium dodecyl sulfate (SDS) (0.5%, 1%, and
3%)-modified soy protein adhesives after water soaking test. Sample
0.5% SDS-SPI 1% SDS-SPI 3% SDS-SPI SPI.sup.a Cherry 33 .+-. 9 49
.+-. 8 32 .+-. 7 -- Pine 31 .+-. 7 41 .+-. 9 33 .+-. 8 6 .+-. 0
Walnut 26 .+-. 8 49 .+-. 6 24 .+-. 8 -- .sup.a Food grade soy
protein isolate available from ADM.
EXAMPLE 10
In conducting the following tests, adhesives having 0.5%, 1%, and
3% by weight of SDBS, respectively, were prepared in a manner
similar to that described in Example 6 with respect to the SDS-SPI
adhesives. Similar tests were conducted on the SDBS specimens as
those described in Examples 6-9 above. This data is reported in
Tables XI-XIV. The SDBS-SPI adhesives showed shear strength
comparable to the SDS-SPI adhesives and superior to that of the
non-modified adhesives, even after the incubation and water soaking
tests. Furthermore, as reported in Table XIII, the SDBS-SPI
specimens exhibited 0% delamination after the water soaking tests
while the non-modified samples demonstrated 90-100%
delamination.
TABLE XI Shear strength (kg/cm.sup.2) of wood specimens glued with
non-modified and sodium dodecylbenzene sulfonate (SDBS) (0.5%, 1%,
and 3%)-modified soy protein adhesives. Sample 0.5% SDBS-SPI 1%
SDBS-SPI 3% SDBS-SPI SPI.sup.a Cherry 55 .+-. 10 58 .+-. 9 33 .+-.
8 41 .+-. 7 Pine 47 .+-. 7 49 .+-. 6 43 .+-. 7 31 .+-. 4 Walnut 50
.+-. 8 51 .+-. 7 36 .+-. 6 30 .+-. 12 .sup.a Food grade soy protein
isolate available from ADM.
TABLE XII Shear strength (kg/cm.sup.2) of wood specimens glued with
non-modified and sodium dodecylbenzene sulfonate (SDBS) (0.5%, 1%,
and 3%)-modified soy protein adhesives after incubation aging test.
Sample 0.5% SDBS-SPI 1% SDBS-SPI 3% SDBS-SPI SPI.sup.a Cherry 48
.+-. 7 53 .+-. 8 31 .+-. 5 38 .+-. 5 Pine 44 .+-. 9 45 .+-. 8 42
.+-. 8 21 .+-. 8 Walnut 44 .+-. 7 48 .+-. 7 27 .+-. 5 25 .+-. 9
.sup.a Food grade soy protein isolate available from ADM.
TABLE XIII Delamination (%) of wood specimens glued with
non-modified and sodium dodecylbenzene sulfonate (SDBS) (0.5%, 1%,
and 3%)-modified soy protein adhesives after water soaking test.
Sample 0.5% SDBS-SPI 1% SDBS-SPI 3% SDBS-SPI SPI.sup.a Cherry 0 0 0
100 Pine 0 0 0 90 Walnut 0 0 0 100 .sup.a Food grade soy protein
isolate available from ADM.
TABLE XIV Shear strength (kg/cm.sup.2) of wood specimens glued with
non-modified and sodium dodecylbenzene sulfonate (SDBS) (0.5%, 1%,
and 3%)-modified soy protein adhesives after water soaking test.
Sample 0.5% SDBS-SPI 1% SDBS-SPI 3% SDBS-SPI SPI.sup.a Cherry 35
.+-. 7 49 .+-. 3 30 .+-. 6 -- Pine 32 .+-. 8 45 .+-. 5 42 .+-. 5 6
.+-. 0 Walnut 23 .+-. 5 48 .+-. 6 23 .+-. 9 -- .sup.a Food grade
soy protein isolate available from ADM.
EXAMPLE 11
In this example, U-SPI adhesives were prepared and shear strength
and delamination properties were determined. Urea solutions (1, 3,
5, and 8 M) were prepared at room temperature. Ten grams of SPI
powder was suspended in each solution (100 ml) with the resulting
suspension being stirred and reacted for 6 hours.
Three wood varieties ranging from hard to soft (walnut, cherry, and
pine) were used. The wood samples were prepared for testing as
described by Kalapathy et al., JAOCS, 72:507-510 (1995),
incorporated by reference herein, with some modifications. Each
wood piece had dimensions of 3 mm.times.20 mm.times.50 mm
(thickness.times.width.times.length). Three pieces of wood were
glued to form a single wood specimen. The modified adhesive slurry
was brushed onto both ends of one wood piece and onto one end of
the remaining two wood pieces. The area of coverage on the ends
receiving adhesive application was 2 cm.times.2 cm to give a
protein concentration of 1.80 mg/cm.sup.2 with a standard deviation
of 0.04 mg/cm.sup.2. After adhesive application, the wood pieces
were allowed to rest at room temperature for about five minutes
after which they were glued together and pressed using a hot press
for about seven minutes under the conditions described in Example
1. The pressed specimens were kept in a plastic bag under ambient
conditions for four days. The test results are set forth in Tables
XV-XVI.
TABLE XV Shear Strength (kg/cm.sup.2) of Wood Specimens Glued with
Non-Modified and Urea (U) (1, 3, 5, and 8 (M))- Modified Soy
Protein Adhesives. Sample 1M U-SPI 3M U-SPI 5M U-SPI 8M U-SPI
SPI.sup.a Walnut 48 .+-. 11 54 .+-. 5 46 .+-. 7 26 .+-. 10 30 .+-.
12 Cherry 42 .+-. 8 59 .+-. 10 37 .+-. 5 33 .+-. 7 41 .+-. 7 Pine
41 .+-. 9 42 .+-. 6 40 .+-. 5 36 .+-. 9 31 .+-. 4 .sup.a
Non-modified soy proteins.
TABLE XVI Shear Strength (kg/cm.sup.2) and Delamination (%) of Wood
Specimens Glued with Non-Modified and Urea (U) (1, 3, 5, and 8
(M))-Modified Soy Protein Adhesives after Incubation Aging and
Water Soaking Tests. Sample 1M U-SPI 3M U-SPI 5M U-SPI 8M U-SPI
SPI.sup.a Shear Strength after Incubation Walnut 49 .+-. 3 45 .+-.
7 33 .+-. 5 21 .+-. 4 25 .+-. 9 Cherry 42 .+-. 7 49 .+-. 11 29 .+-.
8 25 .+-. 7 38 .+-. 5 Pine 41 .+-. 4 39 .+-. 5 31 .+-. 4 21 .+-. 9
21 .+-. 8 Delamination after Water Soaking Walnut 10 0 20 90 100
Cherry 0 0 30 100 100 Pine 0 0 0 0 90 Shear Strength after Water
Soaking Walnut 8 .+-. 2 10 .+-. 2 5 .+-. 1 4 .+-. 0 -- Cherry 12
.+-. 2 14 .+-. 3 7 .+-. 2 -- -- Pine 17 .+-. 2 25 .+-. 3 12 .+-. 2
5 .+-. 1 6 .+-. 0 .sup.a Non-modified soy proteins.
EXAMPLE 12
In this example, guanidine hydrochloride modified SPI adhesives
(GH-SPI) were prepared. GH solutions (0.5, 1, and 3M) were prepared
at room temperature. Ten grams of SPI was suspended in each GH
solutions (100 ml) with the resulting suspension being stirred and
reacted for 6 hours. Wood samples were prepared and adhesives were
applied to those samples as described in Example 11. The same tests
were conducted on the samples as described above with respect to
Example 11. These results are reported in Tables XVII-XVIII.
The GH-SPI adhesives having 0.5M and 1M concentrations of GH
exhibited greater shear strengths than the non-modified control
adhesive. The 1M GH adhesives exhibited the highest shear strength
within each wood category. The 0.5M and 1M GH-modified protein
adhesives exhibited superior shear strengths after the incubation
aging tests and water soaking test and had zero delamination.
TABLE XVII Shear Strength (kg/cm.sup.2) of Wood Specimens Glued
with Non-Modified and Guanidine Hydrochloride (GH) (0.5, 1, and 3
(M))-Modified Soy Protein Adhesives. Sample 0.5M GH-SPI 1M GH-SPI
3M GH-SPI SPI.sup.a Walnut 44 .+-. 7 51 .+-. 6 36 .+-. 5 30 .+-. 12
Cherry 49 .+-. 7 60 .+-. 3 36 .+-. 4 41 .+-. 7 Pine 48 .+-. 3 47
.+-. 6 41 .+-. 4 31 .+-. 4 .sup.a Non-Modified soy proteins.
TABLE XVIII Shear Strength (kg/cm.sup.2) and Delamination (%) of
Wood Specimens Glued with Non-Modified and Guanidine Hydrochloride
(GH) (0.5M, 1M, and 3M)-Modified Soy Protein Adhesives after
Incubation Aging and Water Soaking Tests. Sample 0.5M GH-SPI 1M
GH-SPI 3M GH-SPI SPI.sup.a Shear Strength after Incubation Walnut
41 .+-. 3 38 .+-. 4 32 .+-. 5 25 .+-. 9 Cherry 38 .+-. 5 49 .+-. 5
32 .+-. 4 38 .+-. 5 Pine 40 .+-. 5 37 .+-. 5 42 .+-. 7 21 .+-. 8
Delamination after Water Soaking Walnut 0 0 100 100 Cherry 0 0 100
100 Pine 0 0 0 90 Shear Strength after Water Soaking Walnut 11 .+-.
2 7 .+-. 2 -- -- Cherry 9 .+-. 2 13 .+-. 6 -- -- Pine 20 .+-. 2 37
.+-. 3 9 .+-. 3 6 .+-. 0 .sup.a Non-modified soy proteins.
* * * * *